1. Field of the Invention
The present invention relates to a working vehicle used for gardening maintenance work, agricultural work such as a riding mower and a tractor, and further more construction and transportation work, and, in particular, to a construction of a steering operation device, which is provided with a hydrostatic transmission (hereinafter called “HST”) operating as a travel system speed changer unit, for a vehicle steered by varying respective left and right drive wheels by means of respective left and right levers.
2. Description of the Related Art
A riding mower of a prior art such as Japanese Published Unexamined Patent Application No. 2000-71790 is provided with a pair of HSTs consisting of a hydraulic pump and a hydraulic motor, wherein the output rotations of respective left and right HST hydraulic motors are varied by rotating and operating the trunnion shaft of the hydraulic pump by means of respective left and right steering levers equipped at the control seat side, and the output rotations are transmitted to respective left and right rear wheels for travelling.
However, since, in prior art riding mowers, HST is provided at both left and right sides of the transmission case, respectively, it is necessary that assembly and maintenance work is carried out at both left and right sides of the vehicle, respectively, when manufacturing, performing maintenance, adjusting the HST and/or adjusting the connection between the steering levers and HST pump. Therefore, there is a problem in that work efficiency is not satisfactory.
If the HST hydraulic pump is disposed at one side of the vehicle body, the trunnion shafts of the hydraulic pump are separated to be located forward and rearward, and since the operation shaft centers of the left and right steering levers becomes such that the operation shaft centers oriented in the left and right lateral directions are commonly established, the lengths of the interlock connections to the trunnion shafts differs from each other, wherein the operation feeling in the left and right steering levers become different from each other, and there causes a problem in that it becomes difficult to accurately drive or steer the vehicle for rectilinear propagation.